1. Field of the Invention
The present invention relates to magnetic toner for use in electrophotography, electrostatic recording, magnetic recording, etc.
2. Description of the Related Art
During the transition from analog to digital technology, printers or copying machines have been strongly required in recent years to have excellent latent image reproducibility and a high resolution as well as a compact (small) body and stable image quality in long-term use. First considering the small body, examples of approaches thereto include reduction in the sizes of constituent members of printers and fewer members constituting printers. Particularly, as for toner, examples of the approaches include compact bodies of toner receptacles such as cartridges. For the compact bodies of toner receptacles, a reduced toner consumption per page is strongly demanded. For the reduced toner consumption, it is important to develop toner in just proportion to a latent image.
A single-component contact development method is effective for improving latent image reproducibility as mentioned above. In the conventional single-component contact development method, a developer bearing member and a developer-supplying member are housed in a developing unit. This developer-supplying member can be spared to thereby achieve the reduced toner consumption as well as the more compact body of the toner receptacle.
For sparing the developer-supplying member, effectively, a magnetic field generation unit, for example, is disposed in the inside of the developer bearing member and used in combination with magnetic toner.
A challenge to such a magnetic single-component contact development method without the use of the developer-supplying member, however, is the stabilization of image quality in long-term use. Particularly, a major issue is so-called ghosts, i.e., the difference in developability between after development of a black image and after development of a white background under conditions of low temperature and low humidity (LL).
Approaches based on toner have been practiced in order to stabilize image quality in long-term use. For example, Japanese Patent Application Laid-Open No. 2008-15221 has proposed magnetic toner which specifies a ratio (B/A) of a content (B) of iron atoms to a content (A) of carbon atoms present on the surface of toner and the solubility and amount of dissolution of a magnetic material in toner during dissolution in hydrochloric acid.
Japanese Patent Application Laid-Open No. 2009-229785 has proposed toner for electrostatic latent image development, wherein a ratio HH/HL of a saturated water content HH under conditions of high temperature and high humidity (30° C. and 95% RH) to a saturated water content HL under conditions of low temperature and low humidity (10° C. and 15% RH) is in the range of 1.50 or lower.
In any of these approaches, the toner still has the insufficient stability of image quality, albeit improved to some extent, in long-term use and thus has room for improvement, particularly, in ghosts under conditions of low temperature and low humidity.